Context menu and 'empty folder'
When we select virtual 'empty folder' in on_treeview_selection_changed
os_path == None (error trace)
Need check. I try something like this:
https://github.com/andr7e/meld/commit/965b2c3d13d8aeeeb931a2cccce67232a830afdb#diff-2cbe3c2017155aa09232bc9ec396f162R1119